This invention relates generally to electromagnetic linear motors and deals more specifically with an electromagnetic linear motor having a variable length stroke and providing a substantially large force with both its power stroke and its return stroke.
It is desirable in many instances to utilize a linear motor because it is readily adaptable for integration into the apparatus it is driving to save space.
Another advantage of a linear motor compared to a rotational motor is the elimination of additional mechanisms and apparatus such as, for example, a crankshaft and connecting rod which are normally required to transform rotational motion to linear motion.
It is known to provide an electromagnetic linear motion motor based on the principle of generating a linear force by the interaction of two magnetic fields to cause relative movement between magnetic members. Generally, one of the magnetic fields is produced by one magnetic member such as, a permanent magnet which is generally held stationary relative to another magnetic member such as, an electric coil assembly in which undirectional (DC) current flows to produce the other magnetic field and which assembly is moveable relative to the permanent magnet. The force produced by such an electromagnetic motor is directly proportional to the product of the magnetic flux density produced by the permanent magnet and the magnitude of the current carried by the moving electric coil. Since the magnetic flux density is produced by an unidirectional current, it is of a substantially constant value and the direction of movement and accordingly, force is determined by the directional sense or polarity of the DC current flowing in the electrical coil.
One drawback generally associated with an electromagnetic linear motor of the aforedescribed type is the magnetic flux density produced by a permanent magnet is not of sufficient magnitude to cause an appreciable force and movement of any substantial displacement by the coil assembly relative to the stationary permanent magnet unless the magnet is very large and thus substantially increasing the size of the motor. Consequently, a linear motor using a magnet to produce flux density is in practice, limited to applications wherein a relatively short stroke and small force are required.
Known linear motors that operate on the principal of interactive magnetic fields generally have a short stroke and produce a low force and are unsatisfactory for fluid pumping applications wherein it is required to pump a large volume of fluid at a high rate and/or at a relatively high pressure.
A number of fluid pump apparatus and linear motors have been disclosed wherein the electromagnetic linear motor has a moving coil assembly that generally operates with a large force in one direction of movement only and usually requires a biasing means, such as a spring, to return the moving assembly to its initial starting position from its operated position.
An example of a linear motor and fluid pump apparatus is disclosed in U.S. Pat. No. 2,495,598 to Parker wherein an electromagnet attracts a piston to compress a spring wherein at the end of the stroke the spring returns the piston to its idle position.
Another linear motor and fluid pump apparatus is disclosed in U.S. Pat. No. 2,768,580 to Parker wherein an electromagnet operates to attract a piston to compress a spring and a permanent magnet senses the proximity of the piston during the compression stroke and causes a movable electrical contact to pivot away from a fixed electrical contact to deenergize the electromagnet to permit the spring to return the piston to its normal position. The output of the pump is increased by increasing the compression of the spring through a mechanical adjustment.
All of the known electromagnetic linear motor and fluid pump apparatus have one or more limitations that make them unsuitable for fluid pumping applications.
One limitation generally associated with electromagnetic linear motors of the above-described type that operate by compressing a spring to provide the return stroke or the power stroke require a relatively large spring to generate any appreciable pressure or to pump a large volume of fluid per stroke.
Another limitation generally associated with electromagnetic linear motors and fluid pump apparatus utilizing compression springs is the frequency or repetition rate at which such devices are capable of operating are at relatively low frequencies. When it is desired to operate at a high repetition rate, the spring needed for the return stroke becomes very large and consequently the force needed to compress the spring becomes much greater resulting in slower overall final pressure provided by an associated pump.
A further limitation generally associated with electromagnetic linear motors and fluid pump apparatus in general, is the inability to provide a variable length stroke from stroke-to-stroke and accordingly, to pump a variable volume of fluid from stroke-to-stroke.
It would be desirable, therefore, to provide an electromagnetic linear motor that has a long stroke and a substantially large force in both the power stroke and return stroke that overcomes many of the drawbacks associated with prior electromagnetic linear motor motors.
It is a general object of the present invention therefore, to provide an electromagnetic linear motor that operates on the principal of interactive magnetic fields to move an armature with a reciprocating motion over a relatively large displacement and with a substantially large force in both directions of movement.
It is another object of the present invention to provide an electromagnetic linear motor that is controllable and operates with a variable length stroke.
It is a further object of the present invention to provide an electromagnetic linear motor and an associated central core fluid pump that pumps a variable volume of fluid.
It is a yet further object of the present invention to provide an electromagnetic linear motor and an associated central core fluid pump that operates over a large frequency range.
It is a still further object of the present invention to provide an electromagnetic linear motor and associated central core fluid pump that is usable as a fuel injector for an internal combustion engine.
Other objects and advantages of the invention will be apparent from the following detailed description and from the accompanying drawings forming a part thereof.